NON-ORIENTED ELECTRICAL STEEL SHEET AND METHOD OF MANUFACTURING THE SAME

Abstract

A chemical composition of a base metal of a non-oriented electrical steel sheet contains, by mass %, C: 0.0050% or less, Si: 3.8% to 5.0%, Mn: exceeding 0.2% and less than 2.0%, P: 0.030% or less, S: 0.0030% or less, Al: 0.005% or more and less than 0.050%, N: 0.0005% to 0.0030%, Ti: less than 0.0050%, Nb: less than 0.0050%, Zr: less than 0.0050%, V: less than 0.0050%, Cu: less than 0.20%, Ni: less than 0.50%, Sn: 0% to 0.10%, Sb: 0% to 0.10%, a remainder: Fe and impurities. [Si+0.5×Mn≥4.3] is satisfied and the average grain size of the base metal is in a range of 10 to 80 μm.

Claims

1. A non-oriented electrical steel sheet comprising, as a chemical composition of a base metal, by mass %: C: 0.0050% or less; Si: 3.8% to 5.0%; Mn: exceeding 0.2% and less than 2.0%; P: 0.030% or less; S: 0.0030% or less; Al: 0.005% or more and less than 0.050%; N: 0.0005% to 0.0030%; Ti: less than 0.0050%; Nb: less than 0.0050%; Zr: less than 0.0050%; V: less than 0.0050%; Cu: less than 0.20%; Ni: less than 0.50%; Sn: 0% to 0.10%; Sb: 0% to 0.10%; and a remainder: Fe and impurities, wherein Expression (i) is satisfied, and an average grain size of the base metal is in a range of 10 to 80 μm,
Si+0.5×Mn≥4.3  (i) here, an element symbol in Expression (i) is a content (mass %) of each element.

2. The non-oriented electrical steel sheet according to claim 1, wherein a tensile strength is 650 MPa or more.

3. The non-oriented electrical steel sheet according to claim 1, wherein the chemical composition contains, by mass %, one or two selected from Sn: 0.005% to 0.10% and Sb: 0.005% to 0.10%.

4. The non-oriented electrical steel sheet according to claim 1, further comprising: an insulation coating that is provided on a surface of the base metal.

5. A method of manufacturing the non-oriented electrical steel sheet according to claim 1, the method comprising: performing hot rolling on a steel ingot that has the chemical composition according to claim 1 and then performing the following Step 1 or 2, (Step 1) performing cold rolling and final annealing in order without annealing of a hot-rolled sheet, and (Step 2) performing annealing of a hot-rolled sheet at a temperature of 950° C. or lower and then performing the cold rolling and the final annealing in order, wherein the final annealing is performed in a state where a soaking temperature is in a range of 750° C. to 1000° C. and a soaking time is in a range of 1 to 300 s.

6. The non-oriented electrical steel sheet according to claim 2, wherein the chemical composition contains, by mass%, one or two selected from Sn: 0.005% to 0.10% and Sb: 0.005% to 0.10%.

7. The non-oriented electrical steel sheet according to claim 2, further comprising: an insulation coating that is provided on a surface of the base metal.

Description

EXAMPLES

[0134] Slabs having chemical compositions shown in Table 1 were heated to 1150° C., hot rolling was then performed at a finish temperature of 850° C. and a finish sheet thickness of 2.0 mm, and the slabs were wound at 650° C., so that hot-rolled steel sheets were obtained. At some Test Nos., the obtained hot-rolled steel sheets were annealed at annealing temperatures shown in Table 2 and scale formed on the surfaces of the hot-rolled sheets was removed by pickling. All of soaking times in the annealing of the hot-rolled sheets were set to 30 s. Pickled sheets obtained in this way (pickled sheets from which the scale of the hot-rolled steel sheets were removed in a case where the annealing of the hot-rolled sheets was omitted) were formed into cold-rolled steel sheets having a sheet thickness of 0.25 mm by cold rolling.

[0135] In addition, annealing was performed in a mixed atmosphere in which H.sub.2 was 25%, N.sub.2 was 75%, and a dew point was 0° C. so as to have average grain sizes shown in Table 2 to be described below while final annealing conditions (a soaking temperature (annealing temperature) and a soaking time) were changed. Specifically, in a case where the average grain size was increased, the soaking temperature was set to be higher and/or a soaking time was set to be longer. Further, in a case where the average grain size was decreased, the soaking temperature was set to be lower and/or the soaking time was set to be shorter. Specific soaking temperatures (annealing temperatures) and soaking times are shown in Table 2. After that, an insulation coating was applied to manufacture non-oriented electrical steel sheets and the non-oriented electrical steel sheets were used as test materials.

[0136] Further, an insulation coating consisting of phosphoric acid aluminum and acrylic-styrene copolymer resin emulsion having a grain size of 0.2 μm was applied by a predetermined adhesion amount and was baked in the air at 350° C., so that the insulation coating was formed.

TABLE-US-00001 TABLE 1 Type of Chemical composition (mass %, remainder: Fe and impurities) Left value of steel C Si Mn P S Al N Ti Nb Zr V Cu Ni Sn Sb Expression (i) A 0.0025 3.7 1.4 0.012 0.0008 0.040 0.0012 0.0012 0.0008 0.0007 0.0002 0.062 0.033 0.030 0.001 4.4 B 0.0025 4.2 1.0 0.012 0.0008 0.040 0.0013 0.0013 0.0008 0.0007 0.0018 0.053 0.035 0.028 0.001 4.7 C 0.0020 4.3 1.0 0.013 0.0007 0.040 0.0013 0.0012 0.0009 0.0006 0.0005 0.061 0.050 0.031 0.001 4.8 D 0.0025 4.5 1.0 0.012 0.0009 0.040 0.0012 0.0013 0.0007 0.0004 0.0001 0.058 0.049 0.030 0.001 5.0 E 0.0025 5.1 1.0 0.013 0.0008 0.040 0.0013 0.0012 0.0008 0.0004 0.0006 0.052 0.050 0.030 0.001 5.6 F 0.0018 4.2 0.6 0.015 0.0010 0.031 0.0015 0.0015 0.0014 0.0006 0.0009 0.009 0.006 0.001 0.001 4.5 G 0.0022 4.2 0.6 0.014 0.0009 0.029 0.0015 0.0013 0.0016 0.0006 0.0001 0.005 0.005 0.001 0.025 4.5 H 0.0025 4.2 2.4 0.014 0.0009 0.025 0.0016 0.0012 0.0016 0.0005 0.0001 0.006 0.006 0.001 0.001 5.4 I 0.0021 4.2 0.6 0.045 0.0008 0.028 0.0013 0.0011 0.0014 0.0004 0.0008 0.005 0.006 0.030 0.001 4.5 J 0.0027 4.1 0.8 0.018 0.0010 0.025 0.0015 0.0010 0.0004 0.0001 0.0006 0.012 0.080 0.012 0.015 4.5 K 0.0026 4.3 0.5 0.018 0.0011 0.023 0.0012 0.0011 0.0006 0.0005 0.0004 0.013 0.085 0.026 0.001 4.6 L 0.0023 4.2 0.8 0.012 0.0007 0.031 0.0014 0.0011 0.0006 0.0005 0.0003 0.013 0.092 0.028 0.001 4.6 M 0.0020 4.2 0.4 0.015 0.0010 0.003 0.0012 0.0011 0.0005 0.0005 0.0003 0.012 0.086 0.020 0.001 4.4 N 0.0022 4.2 0.4 0.014 0.0010 0.015 0.0012 0.0012 0.0009 0.0007 0.0005 0.040 0.088 0.022 0.001 4.4 O 0.0029 4.2 0.4 0.014 0.0009 0.100 0.0013 0.0012 0.0009 0.0007 0.0003 0.040 0.085 0.021 0.001 4.4 P 0.0026 4.0 1.0 0.010 0.0010 0.035 0.0014 0.0013 0.0008 0.0008 0.0004 0.051 0.036 0.029 0.001 4.5 Q 0.0022 4.2 0.3 0.011 0.0011 0.015 0.0014 0.0011 0.0010 0.0007 0.0003 0.035 0.020 0.023 0.001 4.4 R 0.0024 4.4 1.4 0.012 0.0007 0.011 0.0012 0.0014 0.0008 0.0006 0.0018 0.050 0.030 0.027 0.001 5.1 S 0.0028 4.2 0.6 0.015 0.0009 0.011 0.0013 0.0010 0.0006 0.0005 0.0004 0.011 0.086 0.011 0.001 4.5 T 0.0027 4.2 0.6 0.010 0.0010 0.015 0.0013 0.0012 0.0008 0.0005 0.0005 0.010 0.080 0.011 0.001 4.5 U 0.0028 4.2 0.6 0.012 0.0010 0.048 0.0014 0.0012 0.0007 0.0005 0.0007 0.012 0.085 0.011 0.001 4.5 V 0.0027 4.2 0.6 0.010 0.0012 0.045 0.0015 0.0013 0.0008 0.0006 0.0007 0.014 0.086 0.011 0.001 4.5 W 0.0026 3.8 0.8 0.013 0.0010 0.020 0.0015 0.0013 0.0009 0.0006 0.0008 0.045 0.033 0.020 0.001 4.2 X 0.0025 4.2 0.2 0.013 0.0010 0.015 0.0012 0.0012 0.0009 0.0007 0.0008 0.052 0.030 0.022 0.001 4.3 Y 0.0025 4.2 0.4 0.012 0.0009 0.060 0.0014 0.0012 0.0006 0.0006 0.0007 0.010 0.085 0.010 0.001 4.4 Z 0.0024 4.4 2.1 0.001 0.0007 0.040 0.0013 0.0013 0.0008 0.0007 0.0016 0.050 0.031 0.028 0.001 5.5

TABLE-US-00002 TABLE 2 Annealing Final annealing Average Test result temperature of Soaking Soaking grain Tensile Test Type of hot-rolled sheet temperature time size strength W.sub.10/400 B.sub.50 No. steel (° C.) (° C.) (s) (μm) (MPa) (W/kg) (T) 1 A 900 950 30 40 613 13.0 1.64 Comparative Example 2 B 900 720 30 8 856 32.3 1.62 Comparative Example 3 B 900 850 30 22 725 16.1 1.63 Present Invention 4 B 900 960 30 52 655 11.9 1 63 Present Invention 5 B 900 1020 30 90 624 11.6 1.62 Comparative Example 6 C 900 980 15 51 669 11.7 1.62 Present Invention 7 D 900 980 15 50 694 11.6 1.61 Present Invention 8 E 900 Fractured during cold rolling Comparative Example 9 F 940 960 15 45 658 12.5 1.63 Present Invention 10 G 940 960 15 45 658 12.6 1.64 Present Invention 11 H 940 960 15 45 684 13.6 1.59 Comparative Example 12 I 940 Fractured during cold rolling Comparative Example 13 J 920 900 15 25 696 15.0 1.64 Present Invention 14 K 920 900 15 25 716 14.8 1.64 Present Invention 15 L Omitted 960 15 35 680 13.5 1.61 Present Invention 16 L 870 950 15 35 680 13.3 1.63 Present Invention 17 L 930 960 15 35 680 13.2 1.64 Present Invention 18 L 990 Fractured during cold rolling Comparative Example 19 M 930 1000 15 55 640 12.4 1.63 Comparative Example 20 N 930 970 15 40 663 12.8 1.63 Present Invention 21 O 930 970 15 60 641 12.0 1.64 Comparative Example 22 P 930 900 15 27 681 15.0 1.64 Present Invention 23 Q 930 900 20 28 651 15.2 1.63 Present Invention 24 R 900 980 20 48 693 12.5 1.60 Present Invention 25 S 930 970 15 50 650 12.4 1.63 Present Invention 26 T 930 970 15 45 655 12.5 1.63 Present Invention 27 U 930 970 15 46 654 12.4 1.63 Present Invention 28 V 930 970 15 40 664 12.8 1.63 Present Invention 29 D 930 750 10 10 782 22.0 1.63 Present Invention 30 D 900 1000 40 80 665 11.4 1.62 Present Invention 31 W 900 750 15 13 662 23.5 1.64 Comparative Example 32 X 900 800 15 20 672 22.5 1.64 Comparative Example 33 Y 930 920 15 38 645 14.4 1.63 Comparative Example 34 Z Omitted 980 20 47 707 12.5 1.58 Comparative Example 35 J Omitted 1010 20 85 635 12.0 1.61 Comparative Example 36 C 930 970 350 86 645 11.5 1.62 Comparative Example 37 C 930 970 300 72 651 11.6 1.62 Present Invention

[0137] The chemical composition of each of the obtained test materials was confirmed using the above-mentioned measurement method. As a result, it could be confirmed that the chemical composition of each of the obtained test materials was substantially the same as the chemical composition of the slab. In addition, the average grain size of the base metal was measured according to JIS G 0551 (2013) “steel-grain size microscopic test method”. Further, Epstein test pieces were taken in a rolling direction and a width direction of each test material, and magnetic characteristics (iron loss W.sub.10/400 and magnetic flux density B.sub.50) were evaluated using Epstein test based on JIS C 2550-1 (2011). A magnetic flux density B.sub.50 of 1.60 T or more was evaluated as an acceptable level and an iron loss W.sub.10/400 of 22.0 W/kg or less was evaluated as an acceptable level. Furthermore, JIS No. 5 tensile test piece was taken from each test material according to JIS Z 2241 (2011) so that a longitudinal direction coincided with the rolling direction of the steel sheet. Then, a tensile test was performed according to JIS Z 2241 (2011) using the above-mentioned test piece to measure a tensile strength. The tensile strength of 650 MPa or more was evaluated as an acceptable level. The above results are also shown in Table 2.

[0138] In Test Nos. 3, 4, 6, 7, 9, 10, 13 to 17, 20, 22 to 30, and 37 in which the chemical composition of a steel sheet and the average grain size thereof after the final annealing satisfy the regulations of the present invention, it was found that the test pieces were excellent in iron loss and magnetic flux density and particularly had low iron loss and a high tensile strength of 650 MPa or more. In particular, in a case where the content of each chemical component has a value within a preferred range, any of these characteristics tended to be further improved.

[0139] In contrast, in Test Nos. 1, 2, 5, 8, 11 to 12, 18, 19, 21, and 31 to 36 that are Comparative examples, at least one of magnetic characteristics and strength was inferior or toughness significantly deteriorates. For this reason, it was difficult to manufacture steel sheets.

[0140] Specifically, a result where a tensile strength was inferior since the Si content was lower than a regulated range in Test No. 1 was obtained. Further, in a case where Test Nos. 2 to 5 in which the chemical composition satisfies regulations were compared with each other, results where iron loss was inferior since the average grain size was smaller than a regulation in Test No. 2 and a tensile strength was inferior since the average grain size was larger than a regulation in Test Nos. 5, 35, and 36 were obtained.

[0141] Further, since the Si content exceeded a regulated range in Test No. 8, the P content exceeded a regulated range in Test No. 12, and the annealing temperature of the hot-rolled sheet exceeded a regulated range in Test No. 18, the steel sheets were fractured during cold rolling due to the deterioration of toughness and the average grain size, a tensile strength, and magnetic characteristics could not be measured. Furthermore, since the Mn content exceeded a regulated range in Test Nos. 11 and 34, results where magnetic flux density was inferior were obtained. Since the Mn content be lower than a regulated range in Test No. 32, a result where iron loss was inferior was obtained.

[0142] Since the Al content was lower than a regulated range in Test No. 19 and the Al content exceeded a regulated range in Test Nos. 21 and 33, it was difficult to adjust the average grain size. Accordingly, results where a tensile strength was inferior were obtained. Since Expression (i) was not satisfied in Test No. 31, a result where iron loss was inferior was obtained.

INDUSTRIAL APPLICABILITY

[0143] As described above, according to the present invention, it is possible to stably obtain a non-oriented electrical steel sheet, which has a high strength and excellent magnetic characteristics, at a low cost.